Two Iowa State University agricultural engineers are studying an old idea for lowering livestock facility odor emissions, but with a new twist.

The idea of pushing the air from building exhaust fans through a biofilter has been around for 40 years or more. Biofilters can be made of many different materials, including compost, straw and wood chips.

Steve Hoff, professor of agricultural and biosystems engineering at Iowa State, said although biofilters are relatively inexpensive to build, most producers reject them because of the added energy costs for continuous operation of exhaust fans through the biofilters.

"We're trying to do some different things with biofilters to make them as cost effective as possible," Hoff said. He is working with Jay Harmon, also a professor in the agricultural and biosystems engineering department, on a project funded by the Iowa Pork Producers Association and a U.S. Department of Agriculture grant. The project has been ongoing for 15 months at a cooperating producer's swine finishing operation near Stratford.

Past research conducted in Minnesota and South Dakota has shown that odors from a livestock production building can be reduced by up to 90 percent when air exhausted from the building moves through a biofilter. The idea Hoff and Harmon are working on is to limit the amount of air treated through a biofilter.

"We don't need to treat the air all the time," Hoff said. "We know odors travel farthest during nighttime, so we filter the amount of exhaust air used during summer evening hours, and only if the atmospheric conditions dictate treatment. But if it's a calm, sunny day, we know odors will disperse quickly and we can bypass the biofilter."

The researchers have developed a system to monitor such things as temperature, humidity, wind speed, wind direction and solar energy. This system automatically controls whether a building's exhaust fans run through the biofilter or bypass it.

"We think we have a good method that will result in effective odor control while being cost effective," Hoff said. "I don't hesitate to tell producers this is something they should consider if the need arises."

Hoff said biofilters can last for several years, so construction costs can be spread out over many groups of pigs.

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